Full-bridge resonant conversion circuit

ABSTRACT

A full-bridge resonant conversion circuit comprises a full-bridge rectification unit, a resonant unit, a first transformer, a second transformer and a synchronous rectification unit, wherein the full-bridge rectification unit comprises a first connection end and a second connection end, the resonant unit comprises a first resonant inductor, a resonant capacitor and a second resonant inductor, the resonant capacitor is connected in series with the first resonant inductor or the second resonant inductor. The first transformer comprises a first primary winding connected in series with the first resonant inductor, and a first secondary winding. Also, the second transformer comprises a second primary winding connected in series with the first primary winding and connected with the second resonant inductor, and a second secondary winding connected in parallel with the first secondary winding, and the synchronous rectification unit is connected with the first secondary winding and the second secondary winding.

FIELD OF THE INVENTION

The invention relates to a full-bridge resonant conversion circuit, inparticular to a full-bridge resonant conversion circuit implemented bydouble transformers.

BACKGROUND OF THE INVENTION

The Chinese invention patents CN 106329940A, CN 103595259B and theChinese utility model patent CN 2063411450 respectively disclose aresonant conversion circuit implemented by double transformers. However,when being used in different power input paths, LLC resonant circuitsadopted in the patents above can produce phase differences at secondarysides of the double transformers connected to a rear end, so that aback-end circuit of the double transformers is not easy to control. Inaddition, since circuits disclosed by the existing patents even causehigh-frequency oscillation at the secondary sides of the doubletransformers, electric components connected at back end of the doubletransformers needs to have relatively high withstanding voltageconditions, and thus the development cost is increased.

SUMMARY OF THE INVENTION

A main object of the present invention is to solve the problems causedby the fact that conventional circuits is likely to produce phasedifferences and high-frequency oscillation at secondary sides oftransformers.

In order to achieve the object above, the present invention provides afull-bridge resonant conversion circuit which comprises a full-bridgerectification unit, a resonant unit, a first transformer, a secondtransformer and a synchronous rectification unit. The full-bridgerectification unit comprises a first connection end and a secondconnection end, the resonant unit comprises a first resonant inductor, aresonant capacitor and a second resonant inductor, wherein the resonantcapacitor is connected in series with the first resonant inductor or thesecond resonant inductor. The first transformer comprises a firstprimary winding connected in series with the first resonant inductor anda first secondary winding magnetically coupled with the first primarywinding. Further, the second transformer comprises a second primarywinding connected in series with the first primary winding and connectedwith one end of the second resonant inductor which is not connected withthe resonant capacitor, and a second secondary winding magneticallycoupled with the second primary winding and connected in parallel withthe first secondary winding, and the synchronous rectification unit isconnected with the first secondary winding and the second secondarywinding.

In an embodiment, the first secondary winding comprises a firstsub-winding, a second sub-winding connected with the first sub-winding,a first output end connected with the first sub-winding, a second outputend connected with the second sub-winding, a first tapped output endconnected between the first sub-winding and the second sub-winding, andthe second secondary winding comprises a third sub-winding, a fourthsub-winding connected with the third sub-winding, a third output endconnected with the third sub-winding, a fourth output end connected withthe fourth sub-winding, and a second tapped output end connected betweenthe third sub-winding and the fourth sub-winding and connected with thefirst tapped output end.

In an embodiment, the polarity of the first sub-winding and the secondsub-winding is the same as the polarity of the first primary winding,and the polarity of the third sub-winding and the fourth sub-winding isthe same as the polarity of the second primary winding.

In an embodiment, the full-bridge rectification unit comprises a firstbridge arm and a second bridge arm, the first bridge arm comprises afirst switch and a second switch connected in series with the firstswitch, the first connection end is formed between the first switch andthe second switch. The second bridge arm comprises a third switch and afourth switch connected in series with the third switch, and the secondconnection end is formed between the third switch and the fourth switch.

In an embodiment, the synchronous rectification unit comprises a powerreference (GND), a power output end connected with the first tappedoutput end and the second tapped output end, a fifth switch connectedwith the first output end and the power reference, and a sixth switchconnected with the second output end and the power reference, a seventhswitch connected with the third output end and the power reference, andan eighth switch connected with the fourth output end and the powerreference.

In an embodiment, the first switch, the second switch, the third switch,the fourth switch, the fifth switch, the sixth switch, the seventhswitch, and the eighth switch are respectively ametal-oxide-semiconductor field-effect transistor (MOSFET).

In an embodiment, the synchronous rectification unit comprises at leastone capacitor connected with the power output end and the powerreference.

Through the embodiments of the present invention above, compared withthe prior art, the present invention has the following characteristics:in the present invention, the first resonant inductor and the secondresonant inductor are symmetrically disposed in the resonant unit, sothat whether power enters from the first connection end or the secondconnection end, the magnetic hysteresis of the first transformer and thesecond transformer are the same. As a result, the output of the firsttransformer and the output of the second transformer do not producephase difference, the control of the synchronous rectification unit isable to be optimized, and then overall efficiency of the full-bridgeresonant conversion circuit is improved. In addition, the circuit of thepresent invention reduces high-frequency oscillation of series loops ofthe first secondary winding and the second secondary winding, therebyreducing the surge generated at the moment when the switches to whichthe synchronous rectification unit belongs is conducted, thewithstanding voltage conditions of the switches to which the synchronousrectification unit belongs are reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit schematic diagram of an embodiment of the presentinvention.

FIG. 2 is a circuit schematic diagram of another embodiment of thepresent invention.

FIG. 3 is a schematic diagram of operating waveforms of a switchdisposed at a secondary side of a transformer according to the presentinvention.

FIG. 4 is a schematic diagram of operating waveforms of a conventionalswitch disposed at the secondary side of the transformer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The detailed description and technical contents of the present inventionwill now be described with reference to the drawings as follows:

Referring to FIG. 1, the present invention provides a full-bridgeresonant conversion circuit 10, which can be used on a power supply or avehicle power system, wherein the power supply may be a power supply ofATX specifications used by the general public, a power supply of aserver, or an industrial power supply. Further, the full-bridge resonantconversion circuit 10 comprises a full-bridge rectification unit 11, aresonant unit 12, a first transformer 13, a second transformer 14, and asynchronous rectification unit 15, wherein the full-bridge rectificationunit 11 serves as a portion for connecting the full-bridge resonantconversion circuit 10 with an external power, and the external power isrectified and provided to a rear-end circuit such as the resonant unit12 after entering the full-bridge rectification unit 11. Further, thefull-bridge rectification unit 11 comprises a first connection end 111and a second connection end 112. It can be understood that the firstconnection end 111 and the second connection end 112 does not serve asthe portion of the full-bridge rectification unit 11 for connecting withthe external power. The full-bridge rectification unit 11 is controlledto output power from the first connection end 111 or the secondconnection end 112. Specifically, in an embodiment, the full-bridgerectification unit 11 comprises a first bridge arm 113 and a secondbridge arm 114, wherein the first bridge arm 113 comprises a firstswitch 115 and a second switch 116 connected in series with the firstswitch 115, the first connection end 111 is formed between the firstswitch 115 and the second switch 116. The second bridge arm 114comprises a third switch 117 and a fourth switch 118 connected in serieswith the third switch 117, and the second connection end 112 is formedbetween the third switch 117 and the fourth switch 118. To prevent DeadTime from occurring, the second switch 116 is cut off when the firstswitch 115 is conducted, and the fourth switch 118 is cut off when thethird switch 117 is conducted. In addition, the first bridge arm 113 andthe second bridge arm 114 are alternately controlled, specifically, whenthe first switch 115 is conducted, the third switch 117 is cut off, andthe fourth switch 118 is conducted. Likewise, when the second switch 116is conducted, the third switch 117 is conducted, and the fourth switch118 is cut off Thus, when the full-bridge rectification unit 11 isimplemented, power is output from the first connection end 111 or thesecond connection end 112 according to control conditions of theswitches 115, 116, 117, and 118. In an embodiment, the first switch 115,the second switch 116, the third switch 117, and the fourth switch 118may be a metal-oxide-semiconductor field-effect transistor (MOSFET),respectively. Furthermore, the first switch 115, the second switch 116,the third switch 117 and the fourth switch 118 are respectivelycontrolled by a control module (not shown in the figure) when beingimplemented.

Further, the resonant unit 12 is an LLC architecture, and the resonantunit 12 is connected with the first connection end 111 and the secondconnection end 112. The resonant unit 12 comprises a first resonantinductor 121, a resonant capacitor 122 and a second resonant inductor123, wherein the resonant capacitor 122 may be connected in series withthe first resonant inductor 121 or the second resonant inductor 123. Forexample, in the embodiment disclosed in FIG. 1, one end of the resonantcapacitor 122 is connected in series with the second resonant inductor123 and the other end of the resonant capacitor 122 is connected withthe second connection end 112. Furthermore, in the embodiment disclosedin FIG. 2, one end of the resonant capacitor 122 is connected in serieswith the first resonant inductor 121 and the other end of the resonantcapacitor 122 is connected with the first connection end 111. On theother hand, the first transformer 13 comprises a first primary winding131 connected in series with the first resonant inductor 121 and a firstsecondary winding 132 magnetically coupled with the first primarywinding 131. Further, the second transformer 14 comprises a secondprimary winding 141 connected in series with the first primary winding131 and connected with the second resonant inductor 123, and a secondsecondary winding 142 magnetically coupled with the second primarywinding 141 and connected in parallel with the first secondary winding132, the first secondary winding 132 and the second secondary winding142 are respectively connected with the synchronous rectification unit15.

Accordingly, the resonant unit 12 of the present invention is providedwith the first resonant inductor 121 and the second resonant inductor123 which are disposed in a symmetrical manner, so that a magnetic pathdistance from the first resonant inductor 121 to the second primarywinding 141 is the same as a magnetic path distance from the secondresonant inductor 123 to the first primary winding 131. Thus, whetherpower enters from the first connection end 111 or the second connectionend 112, the magnetic hysteresis of the first transformer 13 and thesecond transformer 14 are the same. As a result, the output of the firsttransformer 13 and the second transformer 14 do not produce phasedifference, the control of the synchronous rectification unit 15 is ableto be optimized, and then the overall efficiency of the full-bridgeresonant conversion circuit 10 is improved.

Referring again to FIG. 1, in an embodiment, the first secondary winding132 comprises a first sub-winding 133, a second sub-winding 134connected with the first sub-winding 133, a first output end 135connected with the first sub-winding 133, a second output end 136connected with the second sub-winding 134, and a first tapped output end137 connected between the first sub-winding 133 and the secondsub-winding 134. Further, the second secondary winding 142 comprises athird sub-winding 143, a fourth sub-winding 144 connected with the thirdsub-winding 143, a third output end 145 connected with the thirdsub-winding 143, a fourth output end 146 connected with the fourthsub-winding 144, and a second tapped output end 147 connected betweenthe third sub-winding 143 and the fourth sub-winding 144 as well asconnected with the first tapped output end 137. Further, the polarity ofthe first sub-winding 133 and the second sub-winding 134 is the same asthe polarity of the first primary winding 131, and the polarity of thethird sub-winding 143 and the fourth sub-winding 144 is the same as thepolarity of the second primary winding 141.

Accordingly, referring to FIG. 1, in an embodiment, the synchronousrectification unit 15 comprises a power reference 151 (GND), a poweroutput end 152 connected with the first tapped output end 137 and thesecond tapped output end 147, a fifth switch 153 connected with thefirst output end 135 and the power reference 151, a sixth switch 154connected with the second output end 136 and the power reference 151, aseventh switch 155 connected with the third output end 145 and the powerreference 151, and an eighth switch 156 connected with the fourth outputend 146 and the power reference 151. Further, the fifth switch 153, thesixth switch 154, the seventh switch 155, and the eighth switch 156 maybe a metal-oxide-semiconductor field-effect transistor (MOSFET),respectively, wherein the fifth switch 153 is connected with the firstoutput end 135 at a drain electrode (D pole) and connected with thepower reference 151 at a source electrode (S pole). Further, the sixthswitch 154 is connected with the second output end 136 at a drainelectrode (D pole) and connected with the power reference 151 at asource electrode (S pole). Further, the seventh switch 155 is connectedwith the third output end 145 at a drain electrode (D pole) andconnected with the power reference 151 at a source electrode (S pole).Further, the eighth switch 156 is connected with the fourth output end146 at a drain electrode (D pole) and connected with the power reference151 at a source electrode (S pole). Furthermore, the fifth switch 153,the sixth switch 154, the seventh switch 155, and the eighth switch 156are respectively controlled by the control module when beingimplemented.

Accordingly, referring to FIG. 3 and FIG. 4, FIG. 3 is a schematicdiagram of operating waveforms of one of the switches disposed at asecondary side of a transformer according to the present invention, andFIG. 4 is a schematic diagram of operating waveforms of one of switchesdisposed at the secondary side of the transformer of a conventionalcircuit. It is clearly showing from FIG. 3 and FIG. 4 that the circuitof the present invention reduces high-frequency oscillation of seriesloops of the first secondary winding 132 and the second secondarywinding 142, thereby reducing the surge generated at the moment when thefifth switch 153, the sixth switch 154, the seventh switch 155, and theeighth switch 156 are conducted, so that the withstanding voltageconditions of the fifth switch 153, the sixth switch 154, the seventhswitch 155, and the eighth switch 156 are reduced. In addition, Voltages(Vds) between the source electrodes and the drain electrodes of thefifth switch 153, the sixth switch 154, the seventh switch 155, and theeighth switch 156 are balanced by the circuit of the present invention.Furthermore, in an embodiment, the synchronous rectification unit 15comprises at least one capacitor 1157 connected with the power outputend 152 and the power reference 151, wherein the positive pole of the atleast one capacitor 157 is connected with the power output end 152, andthe negative pole of the at least one capacitor 157 is connected withthe power reference 151.

What is claimed is:
 1. A full-bridge resonant conversion circuitcomprising: a full-bridge rectification unit, comprising a firstconnection end and a second connection end; a resonant unit, connectedwith the first connection end and the second connection end, theresonant unit comprising a first resonant inductor, a resonant capacitorand a second resonant inductor; a first transformer, comprising a firstprimary winding connected with the first resonant inductor and a firstsecondary winding magnetically coupled with the first primary winding,wherein the first secondary winding comprises a first sub-winding, asecond sub-winding connected with the first sub-winding, a first outputend connected with the first sub-winding, a second output end connectedwith the second sub-winding, a first tapped output end connected betweenthe first sub-winding and the second sub-winding, and a polarity of eachof the first sub-winding and the second sub-winding is the same as apolarity of the first primary winding; a second transformer, comprisinga second primary winding connected with the first primary winding andconnected with the second resonant inductor, and a second secondarywinding magnetically coupled with the second primary winding andconnected in parallel with the first secondary winding, wherein thesecond secondary winding comprises a third sub-winding, a fourthsub-winding connected with the third sub-winding, a third output endconnected with the third sub-winding, a fourth output end connected withthe fourth sub-winding, a second tapped output end connected between thethird sub-winding and the fourth sub-winding and connected with thefirst tapped output end, and a polarity of each of the third sub-windingand the fourth sub-winding is the same as a polarity of the secondprimary winding; and a synchronous rectification unit, connected withthe first secondary winding and the second secondary winding; whereinthe first resonant inductor, the first primary winding, the secondprimary winding, and the second resonant inductor are sequentiallyconnected in series, the first primary winding and the second primarywinding are directly connected in series without other componenttherebetween, the resonant capacitor is connected in series between thefirst resonant inductor and the first connection end or between thesecond resonant inductor and the second connection end, a polarity endof the first resonant inductor and a polarity end of the second resonantinductor are respectively connected to the resonant capacitor and thefull-bridge rectification unit, and a magnetic path distance from thefirst resonant inductor to the second primary winding is the same as amagnetic path distance from the second resonant inductor to the firstprimary winding.
 2. The full-bridge resonant conversion circuit of claim1, wherein the full-bridge rectification unit comprises a first bridgearm and a second bridge arm, the first bridge arm comprises a firstswitch and a second switch connected in series with the first switch,the first connection end is formed between the first switch and thesecond switch, the second bridge arm comprises a third switch and afourth switch connected in series with the third switch, and the secondconnection end is formed between the third switch and the fourth switch.3. The full-bridge resonant conversion circuit of claim 2, wherein thesynchronous rectification unit comprises a power reference (GND), apower output end connected with the first tapped output end and thesecond tapped output end, a fifth switch connected with the first outputend and the power reference, a sixth switch connected with the secondoutput end and the power reference, a seventh switch connected with thethird output end and the power reference, and an eighth switch connectedwith the fourth output end and the power reference.
 4. The full-bridgeresonant conversion circuit of claim 3, wherein the first switch, thesecond switch, the third switch, the fourth switch, the fifth switch,the sixth switch, the seventh switch, and the eighth switch arerespectively a metal-oxide-semiconductor field-effect transistor(MOSFET).
 5. The full-bridge resonant conversion circuit of claim 1,wherein the synchronous rectification unit comprises a power reference(GND), a power output end connected with the first tapped output end andthe second tapped output end, a fifth switch connected with the firstoutput end and the power reference, a sixth switch connected with thesecond output end and the power reference, a seventh switch connectedwith the third output end and the power reference, and an eighth switchconnected with the fourth output end and the power reference.
 6. Thefull-bridge resonant conversion circuit of claim 5, wherein the fifthswitch, the sixth switch, the seventh switch, and the eighth switch arerespectively a metal-oxide-semiconductor field-effect transistor(MOSFET).
 7. The full-bridge resonant converter circuit of claim 5,wherein the synchronous rectification unit comprises at least onecapacitor connected with the power output end and the power reference.8. The full-bridge resonant conversion circuit of claim 1, wherein thefull-bridge rectification unit comprises a first bridge arm and a secondbridge arm, the first bridge arm comprises a first switch and a secondswitch connected in series with the first switch, the first connectionend is formed between the first switch and the second switch, the secondbridge arm comprises a third switch and a fourth switch connected inseries with the third switch, and the second connection end is formedbetween the third switch and the fourth switch.